There have been known a printer which consecutively prints both sides of a plurality of sheets.
As such printer, there has been proposed a printer in which after an image is formed on one side of a sheet, a discharge roller is rotated in a reverse direction such that the sheet is re-conveyed into a main body casing (switchback conveyance), and an image is formed on the other side of the sheet (for example, JP-A-2011-048328).
Further, in this printer, in order to perform switchback conveyance, a dedicated motor is provided for controlling three states, that is, a state in which the discharge roller and an intermediate discharge roller rotate in their normal rotation directions, a state in which they rotate in their reverse directions, and a state in which they do not rotate. Therefore, at power-on of the printer, an initial mode of the dedicated motor is set, and then an image forming operation is performed.
However, in JP-A-2011-048328, since a plurality of dedicated motors are provided respectively for a discharge unit, an image forming unit, and a conveying unit, the driving sounds of the motors may be generated, and the driving sound of the printer may become louder. In order to reduce the driving sound of the printer, it has been proposed to remove dedicated motors. However, if the dedicated motors are removed, setting of an initial mode by dedicated motors cannot be set, and in order to set an initial mode of a mechanism for performing switchback conveyance at power-on of the printer, it is needed to add a member for detecting an initial mode.
Further, in the printer disclosed in JP-A-2011-048328, as a driving source for various rollers, in addition to a motor for rotating photosensitive drums and developing rollers in one direction and a motor for rotating rollers for conveying sheets toward the image forming unit in one direction, there would be necessary to provide a motor for rotating the discharge roller which switches between a normal rotation and a reverse rotation. Therefore, cost may increase and noise may be generated from the motor sounds.